This tank was developed between 1936 and 1937 by ČKD under the designation of V-8-H as a response to the military demand for a new medium tank. A prototype was trialed in 1938 and after successful conclusion of testing, the Czechoslovak army accepted it in service under the designation of ST vz.39 (medium tank, 1939 pattern). The vehicle had superior firepower compared to early model Panzer III and IV and a mass-production was planned but those plans were ended by the occupation - the Germans tested the protototype with good results but the production of Panzer III and IV was already running. An uparmored variant (under the designation of V8H-Sv) was offered to Sweden in 1942 as well but without success.